From the Departments of Molecular Biology and Medicine, Center for Human Genetic Research, Massachusetts General Hospital, Boston, Massachusetts 02114.

Abstract

We recently identified meclizine, an over-the-counter drug, as an inhibitor of mitochondrial respiration. Curiously, meclizine blunted respiration in intact cells but not in isolated mitochondria, suggesting an unorthodox mechanism. Using a metabolic profiling approach, we now show that treatment with meclizine leads to a sharp elevation of cellular phosphoethanolamine, an intermediate in the ethanolamine branch of the Kennedy pathway of phosphatidylethanolamine biosynthesis. Metabolic labeling and in vitro enzyme assays confirmed direct inhibition of the cytosolic enzyme CTP:phosphoethanolamine cytidylyltransferase (PCYT2). Inhibition of PCYT2 by meclizine led to rapid accumulation of its substrate, phosphoethanolamine, which is itself an inhibitor of mitochondrial respiration. Our work identifies the first pharmacologic inhibitor of the Kennedy pathway, demonstrates that its biosynthetic intermediate is an endogenous inhibitor of respiration, and provides key mechanistic insights that may facilitate repurposing meclizine for disorders of energy metabolism.

Total cellular and mitochondrial phosphatidylethanolamine levels in meclizine-treated fibroblasts. MCH58 fibroblasts were grown in the presence of meclizine (50 μm) or DMSO for 5 h followed by cellular (A) and mitochondrial phospholipid (B) extraction as described under “Experimental Procedures.” Phospholipids were separated using one-dimensional TLC, and phosphorous was quantified using the method of Bartlett (). Data are expressed as the percentage of PE relative to total phospholipids and represent the average of three independent experiments (NS, not significant). Error bars represent S.D.